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An anonymous reader writes "The news last week that exoplanet Gliese 581g may be in the 'Goldilocks zone' and could therefore hold liquid water and alien life got everyone all excited, with good reason. A potentially habitable planet — and only 20 light years away! But to put things in perspective, here are a couple of estimates on what it would take to travel to Gliese 581g. One scientist puts the travel time at 180,000 years based on current space flight technology, while another explains that it could be quite quick if we build a matter-antimatter drive, and can figure out how to bring along 530 times as much mass in fuel as is contained in the ship and cargo itself."

Dave Goldberg, coauthor of A User's Guide to the Universe, took a more optimistic approach. In a blog post, he assumed an average travel speed of 92 percent of the speed of light

That is one HELL of an assumption. Considering that the fastest space vehicles [wikipedia.org] ever created took 3 months to travel a mere 8 light *minutes* (somewhere around one-16000th the speed of light), the assumption that we will ever reach even a significant fraction of the speed of light with a vehicle created anytime in the conceivable future is a bit of an overstretch to say the *least*. At the speed of the Helios probes, that journey to this planet would take over 300,000 years, BTW. So even McConville's 180,000 year estimate is a bit optimistic.

And that's not even throwing in the navigation difficulties (that's going to require some epically precise calculations), the damage such a long trip would inflict to the craft with radiation and micrometeorites, the need for braking when you get there, etc.

Interstellar space is a big VAST empty that few people appreciate. When I was a kid, all the science fiction and popular misinformation made it sound like the next solar system started right at the edge of our own. It was only when I got older that I realized that our solar system is just a tiny dot in a huge sea of lonely empty. The scale of distances between solar systems is difficult for the human mind to even appreciate.

The numbers are truly staggering. I remember my grade school teacher telling us that we would probably one day live to see spaceships traveling to other solar systems. I think now what a silly statement that was, but as a kid I was all "Yeah! Let's go!" All the Star Trek and Star Wars probably didn't help with the popular understanding either (not that they were meant to).

You are correct, but just a mere few hundred years ago the fastest we could move was a dozen or so miles in a day. I am optimistic that if we don't manage to destroy ourselves we'll find means of providing energy and types of propulsion that would seem like magic to us today (kudos to A.C. Clarke for the reference).

I don't think you understand the magnitude of the problem. These are fundamental physical limits of mass and energy we're talking about. Literally the only chance we have of getting to another solar system is to discover an entirely new branch of physics that somehow makes interstellar travel feasible. Probably the best bet is to copy it from visiting aliens, if any ever bother to visit.

And maybe we won't. Ever wonder why we've never visited by aliens? (And I mean an actual visit, with hand-shaking or gun-shooting, not some drunken redneck staring at weather balloons or lights.)

Maybe it's because the gap across stars is too large to cross, and there's simply no science to bridge the distance. Take Star Trek for example. Completely unrealistic. That one scientist says, "...develop a matter-antimatter drive, and can figure out how to bring along 530 times as much mass in fuel as is conta

There is no gap between stars. By the time you get close to exiting our solar system, you will already be closer to a neighboring star then you will be to Sol.

The idea that we will build a ship to go to another star on a direct route is a child's fantasy, much like terraforming Mars. We need to figure out how to live in space. Once we have figured that out, we can go anywhere or nowhere. The resources in space that are close to the Earth dwarf the resources that exist on this planet.

What we need to be working on is automated fabricators and such. Propulsion is over-rated. Just start seeding the path with resources from our automated fabs and then when we do want to go somewhere, we can take our time and not have to bring everything with us.

I liked your take on the gap to the stars. The usual argument goes more along the lines if we get to the next star system and colonize, then make some reasonable assumptions on how easy is would be to recurse and maybe we own the galaxy in 10meg years.

As far as space vs planet, your point has virtue for those who are silly, but you know darn well that we will do both. Who leaves habitat unused? Even the Sahara, which is really sort of an example of the failure so far of whatever,life oriented deity yo

It really is a weird assumption. As if any of us are making a hobby out of hooking up bark controlled shotguns to our dogs. We're a super violent xenophobic ape, it'd be illogical as hell to give that to us unless it came as a double package with genetic engineering for pacifism.

"I don't think you understand the magnitude of the problem." Banks told Cook, "There are fundamental physical limits to the amount of food we can take and the amount of money available to either of us."

Cook wasn't really listening, just looking through the window, already enamouring the feel of the audacious idea. Seeing his friend take but little to no appreciation from his words of warning, Banks continued.

"Literally, the only chance we have of finding another continent is to build an entirely new ship th

Well before we have a fraction of the technology necessary to ship our "ugly bags of mostly water" to another star, we'll likely have hit Kurzweil's Singularity, and most notably the ability to extract and run a Turing image. Even if the computer necessary to run that Turing image is the size of a human body, its "life support" will be electricity and temperature control, the hardware can be slowed down during the boring parts of the journey, it can likely stand higher accelera

Yes, I think tiny self-aware probes will be the way we'll do it. A one-gram probe would still require a Hiroshima to get it to.85c.

You'd be able to launch billions of them, both to target many stars at once, and also to allow the probes to communicate down chains.

You'd be aiming to impact a planet (make it survivable by building the probe mainly out of diamond), after which the nanotech would sprout and build something better. Rather than a simple scatter-gun approach, the probe could steer as it trav

A man on a good horse can maybe cover 30 miles a day unless he wants to kill the horse. A man on foot maybe 20 if he's in top shape. My comment stands. Maybe I should have said "A dozen or few" but still, you're just being pedantic.

Man invented the bit (the thing that goes in a horse's mouth, connected to the reins), which was the technology that allows horses to be tamed and used for transport. This was invented approximately 5,000 years ago and set the maximum speed for humans to around twenty miles per hour (with short bursts up to 50) for almost all of the intervening time. The development of the steam locomotive, around 200 years ago, increased this speed to around 100 miles per hour. After that, the internal combustion engine and the jet made the leap to a few thousand miles per hour in under half a century. Solar sails and nuclear-powered ion drives push this maximum up even further. The rate of change of maximum speed for a human has been increasing a lot over the last few centuries.

I think its funny how many people don't really understand what they are talking about.

Pragmatically, further back that a couple hundred years ago, people rarely traveled. Period. It was largely the aristocracy and wealthy and/or merchants who did the vast majority of traveling. A minority traveled father than twenty to forty miles; and that was typically a city trip for supplies. Its not like in the movies where everyone is constantly traveling around. Traveling to a new area frequently means months to years to become re-established. Its a big, life changing event.

Some exceptions are the military. On foot, on clear terrain, forty to fifty miles were expected. They could do more but would generally be useless for fighting if they did. On horse, with good terrain, calvary would expected to do roughly eighty miles. On rough terrain, a foot soldier was expected to do twenty miles. In heavy forest and/or mountains, snow, etc., ten miles is a good day. Now keep in mind, these guys had heavy equipment they had to carry too, not to mention supplies. And that's really the magic of it all. Having water and food is key. Sure, you *can* travel a much father distance, but being absolutely useless for the next couple of days, assuming you don't die, assuming supplies can catch up, doesn't do anyone any good whatsoever. And don't forget, most places didn't even have roads outside a city. That's one of the things that made Rome great after all.

There are some noteworthy exceptions, such as some of the African tribes who are legendary at running vast distances (example, Zulu) and going right into combat - and winning. But these guys carried only a shield, spear, and absolutely minimum of food and water, and even then, it was war. It was not an everyday event.

Going back to antiquities, it was exceedingly rare to ever travel outside of your valley - again, unless you were a merchant. Realistically, people did not travel. When they did travel, they rarely traveled father than twenty to thirty miles. Those that did travel farther than that, typically had a vocation which required it (merchant, navy, explorer) or a wallet to simply allow for it (summer, winter home). And even then, when they did travel, it was exceedingly rare to be great distances in a day. And of these, ships are the sole exception - until trains - and then cars and planes.

Short version: "Space is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."

That's not true. There's a lot of interstellar hydrogen out there, you can use that as decelerant if you want. Acceleration and deceleration are often assumed symmetric, but that's not required, and given the distribution of resources not even the most effective way to do things.

Emphasis on the "boring" part. Sci-Fi movies have conditioned us to think that space travel would be "start the journey, press the 'hyper-warp-jump' button, watch a light show out the windows for a minute or so and we're there." Instead, unless we discover some radical new way of traveling through space, it'll be "Start the journey, wait anywhere from a thousand to a hundred thousand years and we're* there." (*Where "we're there", really means "our descendents, born aboard the spaceship, are there even t

The Helios probes didn't exactly take 3 months to travel 8 light minutes. I'm not sure where you're getting the numbers, but most likely they mean that the probes took 3 months to get from perihelion to aphelion. The article you linked to on Wikipedia claims their speed record to be 0.000234c, which is over 1/5000th the speed of light, around 3 times the speed you quoted. That's only 100,000 years to go 20 light years. Still impractical.

The theoretical speed for a momentum-limited, 100m orion craft would be 3,3% of the speed of light, so... no. No it wouldn't.

You missed the point completely. 3.3% of the speed of light isn't enough to get there within our lifetimes, but it's a lot faster than the estimate of "180,000 years based on current space flight technology" quoted in the summary.

And make no mistake, Project Orion is completely feasible with present-day technology. The only reason why people avoid mentioning it is because it contains the dirty word "nuclear".

I'd really love to see some college actually do a study on if it would be possible or not. It's hard to say without real research just how much and what kind of resources an ark ship would need over those kinds of timescales. What's the theoretical rate of atmosphere loss? How efficiently can waste be recycled and put back into the ecosystem?

Using a sperm bank to dramatically increase genetic diversity would significantly reduce the minimum size of the crew, an all woman crew would further reduce the size but would probably cause all new problems. A vegan diet reduces the need to support non-human animal mass, but adds a requirement to be able to synthesize some vitamins and proteins. Enough redundant manufacturing to produce spare parts for everything, including the manufacturing facilities. IMO, it looks hard but not impossible with today's technologies.

Let's make sure first that it has, you know, oxygen, and not one of those 95% carbon dyoxide air content some younger planet lacking vegetation may have. Or one of those fancypants sulfuric acid atmospheres that melts your lungs.

The thought occurred to me that perhaps we shouldn't be looking ONLY at earth-sized planets in the goldilocks zone. It seems that a Jupiter or Neptune sized planet in the goldilocks zone could have moons capable of supporting life.

Could we get there? Not by any technology currenly even envisioned. Hell, the Voyager probes are barely past the heliosphere, and they've been travelling for almost 40 years now.

Geek Fail. That page uses the scale from the Next Generation, while Ensign Chekov would obviously have answered using the scale from the original series. By the original series scale [memory-alpha.org], it would take just under 34 days [wolframalpha.com].

Excluding:Mars, Callisto, Ganymede, Europa, Titan, Pluto, Mercury, Iapetus, Miranda, Charon, Eris and a bunch of other "further shores" I have forgotten the names of that are just a tad closer to home.

But I agree on your other point, Gliese 581g is, possibly, a truly profound discovery. If improvements in remote sensing and telescopes reveal that this new world has an Oxygen rich atmosphere or other solid indications of life (radio?) then it will likely be the most profound and culturally altering discove

The planet is 4 times the mass of earth; so because of its gravity, I'd weigh 600 pounds

You are probably just trolling and I'm falling for it by correcting you, but just in case you actually think this. . .

No. Four times the mass does not imply that you would weigh 4 times as much unless the planet's radius is the same as the earth's. That is quite unlikely. A planet with 4 times as much mass as the earth is almost certainly going to be proportionally larger in volume as well. Gravity is proportional to mass, but inversely proportional to the square of the distance from the center of that mass. In the end, if the planet is made of the same sort of rocky material, it will have a similar density, and thus similar gravity.

Would it be exactly 1G? Probably not. Without knowing the planet's volume, we can't know exactly. But a number between.8G and 1.2G is much more likely than 4G.

Of course, I'm assuming that you weigh 150 pounds here on Earth. If you currently weigh 500 pounds, then I apologize. . . your estimated weight on this new world may have been fairly accurate after all.:)

You're forgetting that the volume is proportional to the cube of the radius, while gravity is proportional to the inverse square of the radius. So, while gravity doesn't increase linearly with mass, it's not constant either:

4x mass -> 4x volume -> 4^(1/3)x radius -> 4/4^(2/3)x gravity

So, gravity would be increased about 1.6 times. You should apologize to him if he weighs 380 pounds, not 500.:)

What I find exciting is the prospect of a lot of young minds trying to figure out how to get a probe there with the capability of communicating back (within a reasonable time frame) what it finds. And then the science, if it is a habitable planet, of trying to visit it.

We need a new catalyst to spark imagination and an intense drive to succeed in the sciences.

Even if it is impossible to venture there, the discoveries and new technologies that we _do_ develop that doesn't quite reach the goal, but is above anything we currently have... Exciting!

The biggest design above is the "super" Orion design; at 8 million tons, it could easily be a city.[6] In interviews, the designers contemplated the large ship as a possible interstellar ark. This extreme design could be built with materials and techniques that could be obtained in 1958 or were anticipated to be available shortly after. The practical upper limit is likely to be higher with modern materials.

...

Later studies indicate that the top cruise velocity that can theoretically be achieved by a thermonuclear Orion starship is about 8% to 10% of the speed of light (0.08-0.1c).[1] An atomic (fission) Orion can achieve perhaps 3%-5% of the speed of light. A nuclear pulse drive starship powered by matter-antimatter pulse units would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light.

At 0.1c, Orion thermonuclear starships would require a flight time of at least 44 years to reach Alpha Centauri, not counting time needed to reach that speed (about 36 days at constant acceleration of 1g or 9.8 m/s2). At 0.1c, an Orion starship would require 100 years to travel 10 light years. The late astronomer Carl Sagan suggested that this would be an excellent use for current stockpiles of nuclear weapons.[10]

Project Orion actually calls for the use of nukes at launch, too...on the order of 1000 of them just to get to LEO. So yeah, controlling all of those explosions is pretty highly suspect, considering all we've done is prove that graphite-covered steel spheres can survive a nuclear blast.

A far better plan is colonizing our own Solar System. Perhaps there is an asteroid or moon with sufficient natural resources that it would be better to build and launch the Super Orion from there. Of course, by that time s

For now a matter-antimatter drive might as well be a pipe dream. We don't have a way to create antimatter in any meaningful quantity. Using the current process it would take 2 billion years to produce 1 gram of anti-hydrogen. Then there's storage. Anti-hydrogen has been kept from destroying itself for 10 seconds. (Thanks, Wikipedia.)

Before we start even talking about getting to other planets there are a few things we need to do. We need a space station far more robust than the ISS. One that allows manufacturing in space. Heavy-lift vehicles get all the materials we need into orbit. It's all assembled and launched from space. Needless to say, that's far easier said than done. But if we want to engage in real space exploration I think to start outside of Earth's gravity well. Too much energy is wasted just getting spacecraft into space and building them to survive launch and flight through the atmosphere. Although, I suppose even in space they have to withstand similar loads. But the point is that if you start in space you have many more options.

And I think it's high time we restarted research into nuclear propulsion.

When I first read this, and someone saying it would take 180,000 years to travel there, I thought, "Maybe we can bring that planet to us!"

But then the various issues with this, not least of which that location matters when discussing habitability, struck me and I thought, "Okay, that wouldn't work."

Even if you made a spaceship sized tunnel between here and there, essentially pulling some section of their solar system across the light years to meet with a section of ours...a wormhole if you will...

Extended Heim theory (EHT) is being researched as a possible way to utilize non-propellant methods of interstellar travel, specifically in overcoming the massive distances involved in any space journey. [39][39]http://www.hpcc-space.de/publications/documents/AIAA2010-021-NFF-1.pdf

Current space-travel technology, even accounting for an Orion ship powered by every nuke on Earth, would take so long to get there as to receive a warm welcome by the travelers' own great^N-grandchildren, whose ancestors stayed behind long enough to develop Dilithium Crystals, Warp Drives, and/or whatever technology will whisk travelers there on the order of a few hours.

Sure, chucking a probe 20 lightyears away would be awesome, and if we could scrape together the international will and resources necessary to do that I would be all for such an effort. But what about exploring some of the more exciting areas in our own celestial backyard, if you will?

To date we have only had landers on a few of our planets. We only have functioning rovers on one. We had an impact probe on only one of the moons circling the gas giants. We have rendezvoused with one asteroid, and we have gotten two probes into the Kuiper belt. So, before we go dumping trillions of dollars (and it will cost at least that much) into a tiny (and it will be tiny) scientific payload to another solar system, can we start funding some serious exploration here first?

I want to see landers, rovers, and submersibles on Europa, Enceladus, Titan, Ganymede, Io, and Callisto. I want to see regular sample return missions to near Earth asteroids. I want to start a ferry program between LEO and the Earth's surface for more than a handful of elite astronauts. I want to see experimental habitats on the moon, rovers on Venus, probes on Mercury, orbiters around Jupiter, Saturn, Neptune, Uranus, and even Pluto, and I want to have at least ten more robots actively exploring Mars. Don't get me wrong, Gliese 158g is one hell of an interesting planet and we should study it as best as we can with out long range sensors and, as one 'dotter even suggested, perhaps we should try communicating with it. I see no reason to evens start thinking about sending a matter-based payload to that planet, however, until we really take some time and effort to start exploring our own solar system. For as much as we have done here, we still really don't know all that much about our home system. I, for one, am not convinced that there are not colonies of methane-based life on Titan and a whole city of icy fish people swimming under the crust of Europa. Let's not even start talking about the possible cloud people of Venus or the cave-dwellers of Mars...

I'm with you on most of that, but unfortunately with limited budget we need some priority. Colonizing our Solar System, to me, should be our top priority, so we should focus on the places where we stand the best chance of building permanent habitats in a relatively short time. The moon, obviously, plus Mars, asteroids including especially Ceres and Vesta, Jupiter's Galilean moons (though probably not Io), and Titan for its nitrogen-rich atmosphere. It will be very interesting when our Dawn spacecraft rea

Assuming it takes 100 years to build everything we need to make this flight, by the time you get there it will be 178,570 years after the group that took 1000 years to build the matter/antimatter ship finished their project.

Assuming it takes 100 years to build everything we need to make this flight, by the time you get there it will be 178,570 years after the group that took 1000 years to build the matter/antimatter ship finished their project.

This is what I see happening: The first colony ships will leave for a newly-found planet using then-state-of-the-art technology and when they arrive the first thing they'll see is a McDonald's putting up a sign advertising their new "Colonist Combo Meal Deal".

Your scenario is described in "Songs of Distant Earth" by Arthur C Clarke. In that book, the root of the solar neutrino problem was that the Sun was burning out. Light from the core takes 1000 years to get to the surface, but neutrinos get out practically immediately. The information that the hydrogen-burning life of the Sun was over hadn't made it to the surface yet. So we figured it out, and realized that we had some 900 years (Evidently the solar neutrino problem had barely started when we discovered it.) to find a new home. Interstellar travel became a top priority very quickly. First ships were slower, later ships were faster. The story takes place when an earlier ship stops over at a planet which had already been colonized by a later ship.

Or take "Hitchhiker's Guide" by Douglas Adams or "Those Gentle Voices" by George Alec Effinger. Put all of your non-productive people on the first slow ships. Then those that are left can work faster/better on newer, faster ships. In a twist, safe flight for the first slow ships is optional, as are intentional crashes.

Read Mayflower II, an award-winning, excellent short novel by Stephen Baxter, probably the best contemporary hard Sci-Vi writer. The topic is, indeed a generation ship (one where multiple generations have to pass before the destination is reached). It's absolutely perfectly and vigorously on topic for this entire thread and your post in particular.

That's exactly backwards. Thanks to special relativity, the faster they go, the slower time is passing on earth relative to them.

No you have it backwards. As they approach c their time slows down so that c stays c. Meanwhile on earth time is moving along at 'normal' rates which is much faster than on the ship that is going near c.

The colony ship would only find themselves to have experienced less time than what had passed on earth if they decided to turn around and come back.

Yes because all relativity effects are only felt on the way back. Facepalm. perhaps you meant they would only realize (as in see it firsthand) the time difference when they returned to earth, but they have indeed experienced less time regardless of whether they go back or not.

Listen, this stuff is not easy to articulate, so I will grant that I may not be saying it clearly. But you are leaving out important information in your description, which makes it meaningless from a special relativity standpoint, namely -- relative to what?

As they approach c their time slows down relative to the rest of the universe, earth included so that c stays c. Meanwhile on earth time is moving at at 'normal' rates relative to its own inertial reference frame. That is, as described from the Earth'

Nanomachines can only do all of that stuff because you haven't thought through the problems yet and realized the limitations. How you power a machine that small, or make it intelligent, or give it sensors, or pretty much anything is still a lingering question. Once you get past the sci-fi aspects, nanomachines start to look depressingly limited. Self replicating nanomachines are especially nutty, given how complex such a device would need to be.

I remember leafing through the book "The Science of Star Trek", and thinking that the author simply did not have much imagination. For example, the author assumed that a "transporter" would have to "scan" all of one's atoms, in the way that a fax machine scans a piece of paper. Yet, if teleportation is possible, it probably does not involve scanning: it probably involves some kind of quantum entanglement mechanism - and even that assumption is based on the very limited understanding that we have today of ho